1. Field of the Invention
The present invention relates to a magnetic sensor making use of a magneto-resistive element, to a position sensor incorporating such a magnetic sensor, and to various devices and systems incorporating such a position sensor.
2. Summary of the Prior Art
It is well known that certain materials, known as magneto-resistive materials, have the property of changing their resistance with changes in ambient magnetic fields. By passing a current through such a magneto-resistive element, and monitoring the changes in voltage across the element, it is possible to monitor changes in magnetic fields. Such a magnetic sensor is disclosed in, e.g. JP-A-58-56485 and JP-A-63-96713.
One disadvantage of a magnetic sensor as described above is that accurate measurement is affected by e.g. hysteresis of the magneto-resistive element. Therefore, it has been proposed to form a conductive element immediately adjacent the magneto-resistive element so that one element was superposed on the other. Then, a current was passed through the conductive element, which current generated a magnetic field. Of course, that magnetic field would then affect the magneto-resistive element, and therefore, by varying the currents through the conductive element, and hence the magnetic field generated, it became possible to arrange for the net magnetic field experienced by the magneto-resistive element to remain constant. Hence, the changes in current through the conductor needed to achieve this gave a measurement of the changes in ambient magnetic field.